Tap changers of various designs are well known in the electrical industry. Conventional tap changing mechanisms include a plurality of stationary contact structures which are electrically connected to the tapped windings of the transformer, and a movable contact assembly which may be moved to engage the various stationary contacts. Thus, repositioning the movable contact assembly changes the turns ratio between the windings of the transformer. In the case a 3-phase transformer each phase of the transformer is provided with a separate set of stationary and movable contacts. The movable contacts are usually connected together by a common drive means which causes them to operate in synchronism with each other.
Various means have been used to operate or drive the set of movable contacts. U.S. Pat. Nos. 868,968 and 2,817,247 used a worm gear drive. U.S. Pat. No. 924,295 used a wheel and chain arrangement. U.S. Pat. No. 3,875,354 used a motor and chain drive. A combination of worm gear drive and bell crank is illustrated in U.S. Pat. No. 4,035,717. U.S. Pat. No. 4,013,847 illustrates an arrangement wherein the moving contacts are operated by a rack and pinion. U.S. Pat. No. 3,167,703 used a flexible shaft. Somewhat more complicated arrangements are illustrated in U.S. Pat. Nos.: 1,759,834; 2,009,383; 2,073,579; 3,246,088; 3,247,333; and 3,396,248. Tap changing mechanisms constructed in accordance with the teachings of these earlier patents, often require elaborate coupling mechanisms to change the tap settings. For the most part, the connecting members must be large and rigid to insure proper alignment of the gear drives and to withstand the forces required to change all three phases simultaneously. It also should be clear that, by reducing the mass of metal used in the operating mechanism, the magnetization losses of the transformer will be minimized. Clearly the expense of these earlier schemes cannot be justified if a simpler, easier to operate and easier to maintain mechanism could be used.
In addition to the short comings just described, the overall size and weight of the transformer is increased when such mechanisms are used. The excess space requirements are illustrated by U.S. Pat. Nos.: 1,641,271; 1,641,294; 2,000,754; and 3,467,794.
Moreover, when the voltage of a given polyphase transformer is high and its power output large, the size of such transformers and their associated load tap changing mechanism tend to become intolerably large, often exceeding the size limitations for transportation by rail or truck. Therefor, a tap changing mechanism which is smaller and more economical would be especially desirable.
It also should be clear from an examination of these earlier patents, that the space arrangement between the operating shaft and the drive shaft of the mechanism is often restricted to multiples of 90.degree. when beveled gears and worm gears are used to change the direction of shaft rotation. It would be desirable to have an operating mechanism wherein the axes of rotation would be arranged at angles other than 90.degree. from the direction of rotation of the operating device. This would give the designer greater flexibility and would also reduce the overall size of the apparatus.